PLC Programming Standard IEC 61131

• The IEC 61131 (previously IEC 1131) standard is an effort towards standardizing PLC oriented control. This is more necessary now that personal computers and software are starting to open the PLC market.

• These standards were not designed to force a rigid style, so the different PLC vendors will still have programming environments that vary, but the conceptual elements will be consistent.

• The most notable differences between implementation of PLCs will be addresses of outputs, inputs, internal memory, etc.

• There are a few components to the standard,

IEC 1131-3 Data types and programming

IEC 1131-5 Communications

IEC 1131-7 Fuzzy control

• IEC 1131-3 defines the basic programming languages,

IL (Instruction List): This is effectively mnemonic programming

ST (Structured Text): A BASIC like programming language

LD (Ladder Diagram ): Relay logic diagram based programming

FBD (Function Block Diagram): A graphical dataflow programming method

SFC (Sequential Function Charts): A graphical method for structuring programs

• Many of the functions described in this note set support the standard.